Current commercial jetliners with cargo compartments have fire-suppression systems as a safety feature in the event of a fire in the cargo compartment. The fire-suppression systems typically disperse Halon 1301 (bromotrifluoromethane—CF3Br) as the suppressant. The conventional fire-suppression systems also have multiple bottles of Halon 1301, each with its own discharge mechanism. In the event of a fire in the cargo compartment, fire suppression is achieved by an initial rapid discharge of Halon into the cargo compartment to establish a minimum Halon concentration of 5% or more by volume in the compartment. This initial high Halon concentration level provides effective and fast initial flame knockdown. Sustained fire suppression against deep-seated fire and conflagrations is achieved by maintaining the Halon concentration in the cargo compartment at or above 3%.
The typical fire-suppression systems on large commercial aircraft achieve the initial high Halon concentration level by very quickly releasing the entire contents of one or more high-rate discharge (HRD) bottles of Halon into the cargo compartment. After the HRD bottle(s) are discharged, the Halon concentration peaks and then slowly decreases toward approximately 5% during a period of approximately 20 minutes. In one fire-suppression system used on a Boeing 747-400, two HRD bottles are immediately emptied into a cargo compartment upon activation of the fire-suppression system. The HRD bottles provide approximately 110 pounds of Halon (55 pounds from each HRD bottle) into the cargo compartment to establish an initially high Halon concentration level, which is intended to slowly drop to at least 5%.
The Halon concentration in the cargo compartment is then maintained by providing a substantially continuous, regulated flow of Halon from a plurality of “metered” bottles over an elongated period of time. The metered bottles begin to discharge at a selected time delay after the HRD bottles are discharged. The metered bottles release Halon over an extended time period so the Halon concentration level is maintained at approximately 5%–7%, at least until the aircraft begins its descent to a safe landing.
When a commercial aircraft descends from a cruise altitude, the cargo compartment undergoes a repressurization. The cargo compartment also typically experiences an increase in a compartment leakage rate due to outflow valve effects. The repressurization and increased leakage rate effectively result in additional air being added into the cargo compartment, which causes the Halon concentration to decrease as the aircraft descends.
The conventional fire-suppression systems compensate for the decrease in Halon concentration during descent by maintaining a higher Halon concentration in the cargo compartment during the cruise phase before the descent phase. Accordingly, the Halon concentration level has room to drop as the aircraft descends, while not dropping below the 3% concentration minimum. For example, the metered bottles provide a continuous flow of Halon into the cargo compartment to maintain an elevated Halon concentration level of over 6% through the majority of the aircraft's flight after activation of the fire-suppression system. The Halon concentration level is maintained at this elevated level to compensate for the Halon concentration drop that will occur during descent of the aircraft to a safe landing. Accordingly, the conventional fire-suppression systems, when activated, must contain enough Halon to maintain the intentionally elevated Halon concentration during the flight time prior to descent. The aircraft, therefore, must carry hundreds of pounds of Halon on each flight to ensure that the fire-suppression system will have enough Halon to meet the minimum Halon concentration level requirements at all times in the event a fire condition occurs in one of the cargo compartments. The weight of the Halon negatively impacts the aircraft's fuel efficiency.